[WIP] Actor Group API

[yuyiming]

Documents for Actor Group Design and API:

• Actor Group Design;

Why are these changes needed?

Ray has provided a mechanism for managing individual Actors, while the relationship between Actors is rarely considered in Ray design. It is hard to manipulate multiple Actors as a whole, such as creating 3 Actors in the same physical machine, etc.

This PR introduces Actor Group API, including Placement Group and Life Cycle Group, to manage the placement and the life cycle of Actors in group manner.

[WIP] There is also a common library API called Actor Group in this PR, to which some auto-generated codes are not added yet.

Related issue number

Checks

• I've run scripts/format.sh to lint the changes in this PR.
• I've included any doc changes needed for https://ray.readthedocs.io/en/latest/.
• I've made sure the tests are passing. Note that there might be a few flaky tests, see the recent failure rates at https://ray-travis-tracker.herokuapp.com/.
• Testing Strategy
  • Unit tests
  • Release tests
  • This PR is not tested (please justify below)

[AmplabJenkins]

Can one of the admins verify this patch?

[AmplabJenkins]

Test FAILed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/Ray-PRB/23579/
Test FAILed.

[AmplabJenkins]

Test FAILed.
Refer to this link for build results (access rights to CI server needed):
https://amplab.cs.berkeley.edu/jenkins//job/Ray-PRB/24966/
Test FAILed.

[ericl]

@yuyiming what's the status of this / the supporting Ray core design? Placement groups are very important for us too and we're going to allocate a significant amount of time to help out.

[AmplabJenkins]

Can one of the admins verify this patch?

[ericl]

Going to close these now that we have the real implementation PR out.